Pore structure development of polyacrylonitrile nascent fibers in water stretching process

• Variation of pore structure was determined by thermoporometry during the stretching.
• The glass-transition temperature of PAN nascent fibers in the water was obtained.
• The stretching temperature and ratio affected the movement of molecular chains.
• The movement of molecular chains induced the pore collapse.
• The pore collapse was the main reason for the variation of pore structure.

The effects of stretching temperature and ratio on the pore structure of wet-spun polyacrylonitrile nascent fibers was investigated by thermoporometry (TPM), a calorimetric technique based on lowering liquid triple point temperature inside the pores. The patterns of molecular chain movement were characterized by the tensile recovery. The fibers’ glass-transition temperature determined by the variation of elongation at break at different temperatures was about 75 °C. The pore size distribution (PSD) and pore volume which was determined by the TPM decreased with the stretching temperature and ratio increasing. The reason for the variation of pore structure was the pore collapse, which was characterized by the movement of molecular chains. The stretching temperature and ratio were the two key parameters to induce the molecular chains or microfibrils to move easily. This study also shows that TPM can be used to analyze closed pores of wet-spun nascent fibers inaccessible by other standard porosimetry methods.